This invention relates to filters for water or other liquids, and particularly to a filter assembly which will be rendered partially or wholly inoperative after a predetermined quantity of liquid has passed through the filter media.
Filters are often employed at a point of use in a water supply to remove health threatening contaminants, or to remove undesirable and unpleasant odors or tastes from the water. The point of use filtration is the preferred location because it can remove any contaminants or odors which develop within the distribution system of the residence or building.
One contaminant which is recommended for removal by filters is trihalomethane which is apparently formed by chlorine in the presence of certain organic matter. Activated charcoal is a common filter media which can remove trihalomethane. Activated charcoal is also useful for removing other contaminants and is widely used for removing odors or tastes. One of the problems with the use of activated charcoal filters is that the filter media will become saturated with contaminants and be no longer effective long before any change in the water quality can be detected by the user.
One approach that has been used to signal the saturation of a charcoal filter media involves the use of a flow meter in the line leading from the filter. The flow meter is set for a predetermined total volume representing the capacity of the filter media. When that volume of water has passed through the flow meter, a shut off valve is closed thereby blocking the line. Such flow meters include an impeller rotated by the flow of water or other liquid and gearing connecting the impeller to the shut off valve which is actuated after a predetermined number of rotations by the impeller. Such mechanical devices have some operational drawbacks, and most importantly, the protection which they afford can be defeated by the user by simply resetting the flow meter without replacing the filter media.